The separating of a plug by at least one slit into a plurality of expansion shanks carries with it the disadvantage that the plug may be so deformed when pushed into a borehole provided in the receiving material, e.g. by being kinked or bent, that the plug is prevented from being completely inserted. A mutual displacement of the expansion shanks perpendicularly of the plug axis, especially when the borehole is inaccurately made and is in a soft or non-homogeneous receiving material, deforms the receiving channel within the expansion plug, so that a fastening member can no longer be guided into it along a straight line --that is, centrally. Furthermore, when the expansion shanks are located in a soft receiving material, the insertion of the fastening member, may merely push the shanks outwardly without enabling the threads of a screw to work themselves into the material of the expansion plug to provide a secure attachment therebetween.
These disadvantages are avoided by the expansion plug of the present invention which has expansion shanks connected to each other by at least one parting region or fragible wall means extending lengthwise along the plug and bridging the slit. By means of this connection the expansion plug is considerably more resistant to kinking, bending and torsion, since the expansion shanks cannot become mutually displaced in either the perpendicular or lengthwise direction of the plug axis. These advantages are especially significant when the plug is made of a particularly elastic material, for example rubber.
Since the parting region extends lengthwise along the plug, individual portions of the parting region are, upon insertion of a fastening member such as a screw, successively parted in a zipper-like manner. This enables the receiving channel to be deformed in a novel manner upon insertion of a fastening member into the receiving channel. The expansion shanks progressively distend outwardly and the radial contact pressure builds itself up progressively as the fastening member is inserted lengthwise in the plug. This progressive deformation results in a progressive burying of the parts of the toothlike outer profile in the surrounding receiving material.
The previously known toothlike outer profiles on expansion plugs are formed in a saw-tooth manner, so that one tooth surface runs vertically to the lengthwise axis of the plug, while the other tooth surface is at a relatively sharp angle to it. Vertical tooth surfaces have the disadvantage that upon insertion of the teeth into the receiving material, it is sheared off in certain regions and thereby forms voids by which the bonding of the plug is lessened. This is especially significant for a non-homogeneous receiving material. To avoid this disadvantage, the individual tooth surfaces are curved convexly with different positive opening angles; that is, the tooth surfaces run along the lengthwise axis of the plug at an angle of more than 90.degree.. Due to the convex curvature with positive opening angle, the cutting edge of every tooth on the expansion shanks adjusts itself unhindered during the outward bending of the expansion shank, and does not form a nearly right angle to the lengthwise axis of the plug prior to being placed in the fully distended condition. In this way, there arises a wedge-like insertion of the teeth of the outer profile into the receiving material, so that it is pressed together without shearing. This effect is especially advantageous with the Another feature of the present invention is the arrangement of the tooth-like outer profile. The teeth on each shank are arranged in two rows which are offset with respect to each other, so that every tooth has a side bordering surface running parallel to the lengthwise axis of the plug. This prevents rotation of the plug during setting of the plug into the hole. Moreover, this arrangement of the teeth in the lengthwise plug direction permits a more even distribution of the contact pressure of the plug in the bore of the receiving material.
In order to obtain a good bonding of the expansion plug in an oversized receiving bore prior to the insertion of a fastening member, and to prevent rotation of the expansion plug in the receiving bore upon the beginning of the screwing in of a screw-like fastening member, a further feature of the invention involves the provision of locking tongues. The locking tongues extend outwardly from the shanks at an acute angle to the plug longitudinal axis. From their attachment point to the plug toward the outside, the tongues are narrowed in a wedge shape. Since by the tongues are wider at their base, their bending in a direction along the circumference of the expansion plug is prevented during rotation of a screw. Therefore no stop surface is necessary on the plug which through friction would prevent the tongues from springing outward. It is further advantageous for the outer surface of the tongues to have a curvature corresponding to that of the outer surfaces of the expansion plug, so that in their fully depressed position the tongues do not alter the outer configuration of the plug. This enables the plug to be inserted into a closely dimensioned receiving bore in a hard receiving material.
For firm plug material and/or for locking tongues with a relatively large cross section, the outward resilience of the tongues with reference to the insertion of the expansion plug in a receiving bore may be eased by the provision of a weakening groove in the base region of the tongues.
Yet another advantageous feature of this invention is the arrangement of the receiving channel for a fastening member. The channel runs to near the end of the plug tip and has side surfaces running nearly perpendicularly to the plane of the slit. The channel and slit form a cross-shaped hollow cross section of the plug. From this it follows that a cylindrical fastening member is guided centrally on being pushed or turned into the expansion plug by contact of the four inside edges of this cross-shaped hollow cross section against its perimeter surface with a screw type fastening member, the screw threads cut particularly easily into these inside edges of the expansion plug. This permits the use of screw type fastening members of differing diameter, since there is sufficient material available into which the screw threads can cut and also sufficient hollow cross section presented for displacement of material.
The portions of the slit on opposite sides of the receiving channel are preferably formed with shallow waves. The waves of the slit portions extend along the lengthwise direction of the plug and are a 180.degree. out of phase with each other. A fastening member, upon insertion into the plug alternately comes into contact in the lengthwise direction with the wave crests of the slit, or the inner edges, and yields an enlarged expansion of the plug in a manner in itself known.
The parting regions of the present invention may consist of thin wall portions, which in the region of the inner edge or outer edge of the slits bridge over them. The wall portions hold the expansion shanks together prior to the expansion. The thin wall portions which form the parting regions may be perforated, so that the tearing open of individual segments of the parting regions can occur successively and separately without their influencing each other. The various parting region segments are preferably displaced from each other in the lengthwise direction of the plug.
In order to prevent premature deformation of the expansion plug, that is, premature expansion, three ribs extending in the lengthwise plug direction may be advantageously provided within a cylindrical receiving opening. The plug, the beginning of each of the different ribs is displaced along a thread path in the lengthwise plug direction, so that upon the pushing of a screw type fastening member into the expansion plug, a thread of the fastening member lies against the rib beginnings of the at least three ribs. This prevents premature turning of a screw type fastening member in the slitted region of the expansion plug to a premature expansion. This is a particular advantage for so-called "Durchsteckmontagen." On the other hand, the ribs are not a hindrance to the screwing in of a fastening member, since their beginning corresponds to the pitch of the screw thread.
Briefly described, the invention includes an expansion plug comprising a pair of shanks separated by at least one slit which extends along most of the length of the plug, a receiving channel for a fastener extending along the longitudinal axis of the plug, a plurality of teeth formed by indentations in the outer profile of each of the shanks to anchor the plug in a receiving material, and frangible wall means connecting the shanks across the slit which is relatively long and narrow and extends along the longitudinal axis of the plug.